Picked up my R this past July and slowly over time I'm getting a creaking sound coming from the rear passenger area of the car. It happens when I go over a small bump or driveway where it loads up the opposite corners of the car, like the front right/rear left. The noise doesn't seem to change when I have a rear seat passenger. Anyone have this issue? I need to take it back to the dealer to have this addressed, but I'd like to have an idea of what the issue is.